CBSE Important Questions Class 6 Maths Chapter 5 Prime Time

Prime numbers are numbers greater than 1 that have exactly two factors, 1 and the number itself. Composite numbers have more than two factors, and every whole number greater than 1 has prime factors.

Numbers become easier to study when students can spot factors, multiples, primes and divisibility patterns quickly. CBSE Important Questions Class 6 Maths Chapter 5 helps students practise Prime Time from the 2026 NCERT Ganita Prakash syllabus. The chapter covers common multiples, common factors, prime numbers, composite numbers, co-prime numbers, prime factorisation and divisibility tests. It also uses the idli-vada game, jump-size game and prime puzzles to build number sense for CBSE school exams. The NCERT chapter defines prime numbers as numbers with only two factors and composite numbers as numbers with more than two factors.

Key Takeaways

• Prime Number: A prime number has exactly two factors, 1 and itself.
• Composite Number: A composite number has more than two factors.
• Co-prime Numbers: Two numbers are co-prime when their only common factor is 1.
• Prime Factorisation: Every number greater than 1 can be written as a product of prime numbers.

CBSE Important Questions Class 6 Maths Chapter 5 Structure 2026

Class 6 Maths Chapter 5 Important Questions with Answers

The first skill in Prime Time is to tell whether a number divides another number exactly. These class 6 maths chapter 5 important questions begin with factors, multiples and common multiples.

1. What is a factor of a number?

A factor of a number divides it exactly without leaving a remainder.

1. 4 divides 12 exactly.
2. 12 ÷ 4 = 3.
3. Therefore, 4 is a factor of 12.

Final Answer: A factor divides a number exactly.

2. What is a multiple of a number?

A multiple is a number obtained by multiplying a given number by whole numbers.

1. Multiples of 5 are 5, 10, 15, 20 and 25.
2. Each number comes from 5 × 1, 5 × 2 and so on.
3. Multiples continue endlessly.

Final Answer: Multiples are products of a number with whole numbers.

3. What are common multiples?

Common multiples are multiples shared by two or more numbers.

1. Multiples of 3 include 3, 6, 9, 12, 15.
2. Multiples of 5 include 5, 10, 15, 20.
3. 15 is common to both lists.

Final Answer: 15 is a common multiple of 3 and 5.

4. What are common factors?

Common factors are factors shared by two or more numbers.

1. Factors of 20 are 1, 2, 4, 5, 10, 20.
2. Factors of 28 are 1, 2, 4, 7, 14, 28.
3. Common factors are 1, 2 and 4.

Final Answer: Common factors of 20 and 28 are 1, 2 and 4.

5. Find all multiples of 40 between 310 and 410.

The multiples of 40 between 310 and 410 are 320, 360 and 400.

1. 40 × 8 = 320.
2. 40 × 9 = 360.
3. 40 × 10 = 400.

Final Answer: 320, 360, 400

6. Find the common factors of 35 and 50.

The common factors of 35 and 50 are 1 and 5.

1. Factors of 35 are 1, 5, 7, 35.
2. Factors of 50 are 1, 2, 5, 10, 25, 50.
3. The common factors are 1 and 5.

Final Answer: 1 and 5

Prime Time Class 6 Questions on Idli-Vada Game

The idli-vada game turns common multiples into a number pattern. In Prime Time class 6 questions, students use multiples of 3, 5 and other pairs to predict common turns.

7. In the idli-vada game, when should players say “idli”?

Players say “idli” for multiples of 3.

1. Multiples of 3 are 3, 6, 9, 12 and 15.
2. These numbers come after equal jumps of 3.
3. Some of these may also be multiples of 5.

Final Answer: Players say “idli” for multiples of 3.

8. In the idli-vada game, when should players say “vada”?

Players say “vada” for multiples of 5.

1. Multiples of 5 are 5, 10, 15, 20 and 25.
2. These numbers come after equal jumps of 5.
3. Some of these may also be multiples of 3.

Final Answer: Players say “vada” for multiples of 5.

9. When should players say “idli-vada”?

Players say “idli-vada” for common multiples of 3 and 5.

1. 15 is a multiple of 3.
2. 15 is also a multiple of 5.
3. Therefore, 15 is the first idli-vada number.

Final Answer: Players say “idli-vada” at 15, 30, 45 and so on.

10. At what number is “idli-vada” said for the 10th time?

“Idli-vada” is said for the 10th time at 150.

1. Common multiples of 3 and 5 are multiples of 15.
2. The 10th multiple of 15 is 15 × 10.
3. 15 × 10 = 150.

Final Answer: 150

11. If the game is played from 1 to 90, how many times is “idli” said?

“Idli” is said 30 times from 1 to 90.

1. Count multiples of 3 up to 90.
2. 90 ÷ 3 = 30.
3. This count includes idli-vada turns.

Final Answer: 30 times

12. If the game is played from 1 to 90, how many times is “vada” said?

“Vada” is said 18 times from 1 to 90.

1. Count multiples of 5 up to 90.
2. 90 ÷ 5 = 18.
3. This count includes idli-vada turns.

Final Answer: 18 times

13. If the game is played from 1 to 90, how many times is “idli-vada” said?

“Idli-vada” is said 6 times from 1 to 90.

1. Idli-vada numbers are multiples of 15.
2. Count multiples of 15 up to 90.
3. 90 ÷ 15 = 6.

Final Answer: 6 times

14. If the idli-vada game is played till 900, how many times is “idli-vada” said?

“Idli-vada” is said 60 times till 900.

1. Idli-vada numbers are multiples of 15.
2. Count multiples of 15 up to 900.
3. 900 ÷ 15 = 60.

Final Answer: 60 times

Factors and Multiples Class 6 Extra Questions

The jump-size game shows why common factors matter. These factors and multiples class 6 questions help students connect games with exact division.

15. What jump sizes will land on 24?

The jump sizes that land on 24 are the factors of 24.

1. Factors of 24 are 1, 2, 3, 4, 6, 8, 12 and 24.
2. Each jump size divides 24 exactly.
3. Jumpy reaches 24 using these jump sizes.

Final Answer: 1, 2, 3, 4, 6, 8, 12, 24

16. What jump sizes will land on both 14 and 36?

The jump sizes that land on both 14 and 36 are 1 and 2.

1. Factors of 14 are 1, 2, 7, 14.
2. Factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, 36.
3. Common factors are 1 and 2.

Final Answer: 1 and 2

17. What jump sizes will land on both 15 and 30?

The jump sizes that land on both 15 and 30 are 1, 3, 5 and 15.

1. Factors of 15 are 1, 3, 5, 15.
2. Factors of 30 are 1, 2, 3, 5, 6, 10, 15, 30.
3. Common factors are 1, 3, 5 and 15.

Final Answer: 1, 3, 5, 15

18. What jump sizes will land on both 28 and 70?

The jump sizes that land on both 28 and 70 are 1, 2, 7 and 14.

1. Factors of 28 are 1, 2, 4, 7, 14, 28.
2. Factors of 70 are 1, 2, 5, 7, 10, 14, 35, 70.
3. Common factors are 1, 2, 7 and 14.

Final Answer: 1, 2, 7, 14

19. Find a perfect number between 1 and 10.

The perfect number between 1 and 10 is 6.

1. Factors of 6 are 1, 2, 3 and 6.
2. Their sum is 1 + 2 + 3 + 6 = 12.
3. Twice the number is 2 × 6 = 12.

Final Answer: 6

20. Find three multiples of 25 that are not multiples of 50.

Three such numbers are 25, 75 and 125.

1. Each number is divisible by 25.
2. None of them ends in 00 or 50.
3. Therefore, they are not multiples of 50.

Final Answer: 25, 75, 125

Prime Numbers Class 6 and Composite Numbers Class 6 Questions

Prime and composite numbers help students understand how numbers break into factors. The NCERT chapter states that 1 is neither prime nor composite.

21. What is a prime number?

A prime number is a number with exactly two factors, 1 and itself.

1. 7 has factors 1 and 7.
2. It has no other factor.
3. Therefore, 7 is prime.

Final Answer: A prime number has exactly two factors.

22. What is a composite number?

A composite number has more than two factors.

1. 12 has factors 1, 2, 3, 4, 6 and 12.
2. It has more than two factors.
3. Therefore, 12 is composite.

Final Answer: A composite number has more than two factors.

23. Is 1 a prime number or composite number?

1 is neither prime nor composite.

1. A prime number has exactly two factors.
2. A composite number has more than two factors.
3. 1 has only one factor.

Final Answer: 1 is neither prime nor composite

24. Is 2 a prime number?

Yes, 2 is a prime number.

1. Factors of 2 are 1 and 2.
2. It has exactly two factors.
3. It is also the only even prime number.

Final Answer: 2 is prime

25. Is there any even prime number other than 2?

No, there is no even prime number other than 2.

1. Every even number greater than 2 is divisible by 2.
2. Such numbers have more than two factors.
3. Therefore, they are composite.

Final Answer: 2 is the only even prime number

26. Which numbers are prime: 23, 51, 37 and 26?

23 and 37 are prime numbers.

1. 23 has only two factors, 1 and 23.
2. 37 has only two factors, 1 and 37.
3. 51 and 26 have more than two factors.

Final Answer: 23 and 37

27. How many prime numbers are there from 21 to 30?

There are two prime numbers from 21 to 30.

1. The prime numbers are 23 and 29.
2. Other numbers in this range are composite.
3. 21 and 27 are divisible by 3.

Final Answer: 2 prime numbers

28. How many composite numbers are there from 21 to 30?

There are eight composite numbers from 21 to 30.

1. Prime numbers in the range are 23 and 29.
2. The remaining eight numbers are composite.
3. These are 21, 22, 24, 25, 26, 27, 28 and 30.

Final Answer: 8 composite numbers

Sieve of Eratosthenes Class 6 Questions

The sieve of Eratosthenes class 6 method lists primes by crossing out multiples. It starts by crossing out 1 because 1 is neither prime nor composite.

29. What is the Sieve of Eratosthenes?

The Sieve of Eratosthenes is a method used to find prime numbers.

1. Cross out 1 first.
2. Circle the first uncrossed number.
3. Cross out its multiples.
4. Continue until all numbers are checked.

Final Answer: It is a method for listing prime numbers.

30. Why is 1 crossed out in the Sieve of Eratosthenes?

1 is crossed out because it is neither prime nor composite.

1. It has only one factor.
2. A prime number needs exactly two factors.
3. A composite number needs more than two factors.

Final Answer: 1 is not counted as prime or composite.

31. Why are multiples of 2 crossed out after circling 2?

Multiples of 2 are crossed out because they are divisible by 2.

1. 2 is prime.
2. Multiples of 2 greater than 2 have at least three factors.
3. Therefore, they are composite.

Final Answer: Multiples of 2 greater than 2 are composite.

32. What are twin primes?

Twin primes are pairs of prime numbers that differ by 2.

1. 3 and 5 are prime numbers.
2. Their difference is 2.
3. Therefore, 3 and 5 are twin primes.

Final Answer: Twin primes differ by 2.

33. Write the twin primes between 1 and 100.

The twin primes between 1 and 100 are 3 and 5, 5 and 7, 11 and 13, 17 and 19, 29 and 31, 41 and 43, 59 and 61, and 71 and 73.

1. Each pair contains prime numbers.
2. Each pair has a difference of 2.
3. No composite number appears in the list.

Final Answer: (3,5), (5,7), (11,13), (17,19), (29,31), (41,43), (59,61), (71,73)

34. Find seven consecutive composite numbers between 1 and 100.

Seven consecutive composite numbers are 90, 91, 92, 93, 94, 95 and 96.

1. None of these numbers is prime.
2. Each has more than two factors.
3. They appear one after another.

Final Answer: 90, 91, 92, 93, 94, 95, 96

35. Is every even number composite?

No, every even number is not composite because 2 is prime.

1. 2 is even.
2. 2 has exactly two factors.
3. Every even number greater than 2 is composite.

Final Answer: The statement is false.

Co-prime Numbers Class 6 Important Questions

Two numbers can be “safe” in the treasure game when no jump size except 1 reaches both. This is the idea behind co-prime numbers class 6.

36. What are co-prime numbers?

Co-prime numbers are numbers that have no common factor other than 1.

1. Factors of 4 are 1, 2 and 4.
2. Factors of 9 are 1, 3 and 9.
3. Their only common factor is 1.

Final Answer: 4 and 9 are co-prime.

37. Are 15 and 39 co-prime?

No, 15 and 39 are not co-prime.

1. Factors of 15 include 3.
2. Factors of 39 include 3.
3. They have a common factor other than 1.

Final Answer: No

38. Are 4 and 15 co-prime?

Yes, 4 and 15 are co-prime.

1. Factors of 4 are 1, 2 and 4.
2. Factors of 15 are 1, 3, 5 and 15.
3. Their only common factor is 1.

Final Answer: Yes

39. Which pairs are co-prime: 18 and 35, 15 and 37, 30 and 415, 17 and 69, 81 and 18?

The co-prime pairs are 18 and 35, 15 and 37, and 17 and 69.

1. These pairs have no common factor other than 1.
2. 30 and 415 share 5.
3. 81 and 18 share 3 and 9.

Final Answer: 18 and 35, 15 and 37, 17 and 69

40. Are any two prime numbers co-prime?

Yes, any two different prime numbers are co-prime.

1. A prime has only 1 and itself as factors.
2. Two different primes do not share each other as factors.
3. Their only common factor is 1.

Final Answer: Different prime numbers are co-prime.

41. When is the first common multiple equal to the product of two numbers?

The first common multiple equals the product when the two numbers are co-prime.

1. 3 and 5 are co-prime.
2. Their product is 3 × 5 = 15.
3. Their first common multiple is also 15.

Final Answer: This happens for co-prime pairs.

Prime Factorisation Class 6 Questions with Answers

Prime factorisation breaks a number into prime factors only. The NCERT chapter states that every number greater than 1 has prime factorisation.

42. What is prime factorisation?

Prime factorisation is writing a number as a product of prime numbers.

1. 56 = 2 × 2 × 2 × 7.
2. All factors in this product are prime.
3. Therefore, this is the prime factorisation of 56.

Final Answer: Prime factorisation writes a number as a product of primes.

43. Find the prime factorisation of 64.

The prime factorisation of 64 is 2 × 2 × 2 × 2 × 2 × 2.

1. 64 = 2 × 32.
2. 32 = 2 × 16.
3. Continue until only 2s remain.

Final Answer: 64 = 2 × 2 × 2 × 2 × 2 × 2

44. Find the prime factorisation of 105.

The prime factorisation of 105 is 3 × 5 × 7.

1. 105 is divisible by 3.
2. 105 ÷ 3 = 35.
3. 35 = 5 × 7.

Final Answer: 105 = 3 × 5 × 7

45. Find the prime factorisation of 243.

The prime factorisation of 243 is 3 × 3 × 3 × 3 × 3.

1. 243 ÷ 3 = 81.
2. 81 = 3 × 3 × 3 × 3.
3. Therefore, 243 has five factors of 3.

Final Answer: 243 = 3 × 3 × 3 × 3 × 3

46. Find the prime factorisation of 1000.

The prime factorisation of 1000 is 2 × 2 × 2 × 5 × 5 × 5.

1. 1000 = 10 × 100.
2. 10 = 2 × 5.
3. 100 = 2 × 2 × 5 × 5.

Final Answer: 1000 = 2 × 2 × 2 × 5 × 5 × 5

47. The prime factorisation has one 2, two 3s and one 11. Find the number.

The number is 198.

1. Multiply the given prime factors.
2. 2 × 3 × 3 × 11 = 198.
3. Therefore, the number is 198.

Calculation:
2 × 3 × 3 × 11 = 198

Final Answer: 198

48. Find three prime numbers less than 30 whose product is 1955.

The three prime numbers are 5, 17 and 23.

1. 1955 ends in 5, so it is divisible by 5.
2. 1955 ÷ 5 = 391.
3. 391 = 17 × 23.

Final Answer: 5, 17, 23

49. Find the smallest number whose prime factorisation has three different prime numbers.

The smallest number is 30.

1. Take the three smallest prime numbers.
2. They are 2, 3 and 5.
3. 2 × 3 × 5 = 30.

Final Answer: 30

50. Find the smallest number whose prime factorisation has four different prime numbers.

The smallest number is 210.

1. Take the four smallest prime numbers.
2. They are 2, 3, 5 and 7.
3. 2 × 3 × 5 × 7 = 210.

Final Answer: 210

Product of Primes Class 6 and Divisibility by Prime Factorisation

Prime factorisation helps students check co-prime pairs and divisibility without long division. These product of primes class 6 questions train exact factor checking.

51. Are 56 and 63 co-prime?

No, 56 and 63 are not co-prime.

1. 56 = 2 × 2 × 2 × 7.
2. 63 = 3 × 3 × 7.
3. Both have 7 as a common prime factor.

Final Answer: No

52. Are 80 and 63 co-prime?

Yes, 80 and 63 are co-prime.

1. 80 = 2 × 2 × 2 × 2 × 5.
2. 63 = 3 × 3 × 7.
3. They have no common prime factor.

Final Answer: Yes

53. Is 168 divisible by 12 using prime factorisation?

Yes, 168 is divisible by 12.

1. 168 = 2 × 2 × 2 × 3 × 7.
2. 12 = 2 × 2 × 3.
3. The prime factorisation of 12 is included in that of 168.

Final Answer: 168 is divisible by 12

54. Is 75 divisible by 21 using prime factorisation?

No, 75 is not divisible by 21.

1. 75 = 3 × 5 × 5.
2. 21 = 3 × 7.
3. 7 is not a prime factor of 75.

Final Answer: 75 is not divisible by 21

55. Is 42 divisible by 12 using prime factorisation?

No, 42 is not divisible by 12.

1. 42 = 2 × 3 × 7.
2. 12 = 2 × 2 × 3.
3. 12 needs two 2s, but 42 has only one 2.

Final Answer: 42 is not divisible by 12

56. Are 30 and 45 co-prime?

No, 30 and 45 are not co-prime.

1. 30 = 2 × 3 × 5.
2. 45 = 3 × 3 × 5.
3. They share 3 and 5.

Final Answer: No

57. Are 343 and 216 co-prime?

Yes, 343 and 216 are co-prime.

1. 343 = 7 × 7 × 7.
2. 216 = 2 × 2 × 2 × 3 × 3 × 3.
3. They have no common prime factor.

Final Answer: Yes

Divisibility Tests Class 6 Important Questions

Divisibility tests help students check factors of large numbers quickly. In divisibility tests class 6, the NCERT chapter focuses on tests for 10, 5, 2, 4 and 8.

58. What is the divisibility test for 10?

A number is divisible by 10 if its units digit is 0.

1. 8560 ends in 0.
2. Numbers ending in 0 are multiples of 10.
3. Therefore, 8560 is divisible by 10.

Final Answer: A number ending in 0 is divisible by 10.

59. What is the divisibility test for 5?

A number is divisible by 5 if its units digit is 0 or 5.

1. 125 ends in 5.
2. 8560 ends in 0.
3. Both are divisible by 5.

Final Answer: Units digit 0 or 5 means divisible by 5.

60. What is the divisibility test for 2?

A number is divisible by 2 if its units digit is 0, 2, 4, 6 or 8.

1. 682 ends in 2.
2. 8560 ends in 0.
3. Both are divisible by 2.

Final Answer: Even units digits show divisibility by 2.

61. What is the divisibility test for 4?

A number is divisible by 4 if the number formed by its last two digits is divisible by 4.

1. In 8536, the last two digits form 36.
2. 36 is divisible by 4.
3. Therefore, 8536 is divisible by 4.

Final Answer: Last two digits must form a number divisible by 4.

62. What is the divisibility test for 8?

A number is divisible by 8 if the number formed by its last three digits is divisible by 8.

1. In 8560, the last three digits form 560.
2. 560 is divisible by 8.
3. Therefore, 8560 is divisible by 8.

Final Answer: Last three digits must form a number divisible by 8.

63. Is 14560 divisible by 2, 4, 5, 8 and 10?

Yes, 14560 is divisible by 2, 4, 5, 8 and 10.

1. It ends in 0, so it is divisible by 2, 5 and 10.
2. Last two digits 60 are divisible by 4.
3. Last three digits 560 are divisible by 8.

Final Answer: Yes

64. Which numbers are divisible by all of 2, 4, 5, 8 and 10: 572, 2352, 5600, 6000, 77622160?

The numbers are 5600, 6000 and 77622160.

1. Each ends in 0, so it is divisible by 2, 5 and 10.
2. Their last two digits are divisible by 4.
3. Their last three digits are divisible by 8.

Final Answer: 5600, 6000, 77622160

65. Write two numbers whose product is 10000 and whose units digits are not 0.

The two numbers can be 16 and 625.

1. 16 does not end in 0.
2. 625 does not end in 0.
3. 16 × 625 = 10000.

Final Answer: 16 and 625

Class 6 Maths Chapter 5 Extra Questions for CBSE Practice

These class 6 maths chapter 5 extra questions mix MCQs, true-false and reasoning. They match the CBSE 2026 school exam style for Prime Time.

66. True or False: A product of two prime numbers can be prime.

False, a product of two prime numbers is composite.

1. Example: 2 × 3 = 6.
2. 6 has more than two factors.
3. Therefore, it is composite.

Final Answer: False

67. True or False: Prime numbers do not have any factors.

False, prime numbers have exactly two factors.

1. Every prime has factor 1.
2. Every prime has itself as a factor.
3. These are exactly two factors.

Final Answer: False

68. True or False: There is no prime number whose units digit is 4.

True, no prime number has units digit 4.

1. A number ending in 4 is even.
2. Every even number greater than 2 is composite.
3. 2 does not end in 4.

Final Answer: True

69. Which number is the product of exactly three distinct prime numbers: 45, 60, 91, 105, 330?

105 is the product of exactly three distinct prime numbers.

1. 105 = 3 × 5 × 7.
2. The three prime factors are distinct.
3. Other options do not match this condition.

Final Answer: 105

70. How many three-digit prime numbers can be made using 2, 4 and 5 once each?

No three-digit prime number can be made using 2, 4 and 5 once each.

1. Any number ending in 2 or 4 is even.
2. Any number ending in 5 is divisible by 5.
3. All possible arrangements are composite.

Final Answer: 0

71. Find two primes where doubling one and adding 1 gives another prime.

One example is 5 and 11.

1. Start with prime 5.
2. 2 × 5 + 1 = 11.
3. 11 is also prime.

Final Answer: 5 gives 11

72. Find the smallest number that is a multiple of all numbers from 1 to 10.

The smallest number is 2520.

1. It must contain enough prime factors for 1 to 10.
2. 2520 is divisible by 2, 3, 4, 5, 6, 7, 8, 9 and 10.
3. No smaller positive number satisfies all these conditions.

Final Answer: 2520

Important Questions Class 6 Maths: